Pin plugin Runner cleanup to its physical task (#19300)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Plugin Runner owners manage a physical task through an environment
lease.
> - The existing replacement path can assign a new physical task to that
same lease.
> - A delayed old owner can then stop the replacement or mark it
stopped.
> - Cleanup must keep the original physical task identity across RPC and
database writes.
> - This pull request pins that identity and keeps cleanup available to
the new owner.

## Linked Issues or Issue Description

Refs #19134 and #19157. This fix is based on master and does not enable
repeated stopped-source recovery. A search found no duplicate fix.

**What happened?**

The maintained `createOwnedSandbox` replacement path changes
`providerLeaseId` on one lease. An old task owner uses that mutable
lease for a later Stop. A stopped-state response already in flight can
also update the new task's flags.

**Expected behavior**

The old owner must address its original task. Its late cleanup writes
must not alter the replacement. The replacement's own owner must still
stop and complete it.

**Steps to reproduce**

1. Create a plugin task owner for a stopped task.
2. Replace that task through the existing describe/startup path on the
same lease.
3. Resume an old checkpoint or a held old status response.
4. Observe a Stop for the replacement or an incorrect stopped flag
before this fix.

## What Changed

- Require each task owner to keep the physical ID returned by its
description. Reject a rebind to a different task.
- Carry the ID through the existing internal task context after startup
ends. Reject a changed physical task before RPC dispatch.
- Match the physical task in stopped-state, completion and
credential-handoff writes.
- Hold the exact lease row through the retained-session database update
and local checkpoint save.
- Cover the maintained replacement path with real PostgreSQL tests.
Preserve positive cleanup for the replacement owner. Document this
boundary.

## Verification

- Both replacement regressions failed on unmodified master `10a7d039c8`:
delayed old-owner Stop targeted the replacement, and a held old status
response marked it stopped.
- Six focused files passed 160 tests: task authority, task runtime, warm
tasks, execution target, credential writeback and task owner.
- Four selected executor factory cases passed. They cover task-only
providers and the physical task binding after the startup context ends.
- Runner TypeScript, plugin SDK and adapter-utils builds passed. Server
TypeScript check passed. Diff and added-line secret scans passed.
- All 15 setup-probe cases passed with the actual Runner and fake
provider binaries. The first local attempt lacked cargo on PATH. A
sandboxed native attempt timed out in seven process cases; the unchanged
run with loopback permission passed all 15. A separate initial DB
integration attempt was denied a loopback listener; its
permission-correct run passed.
- Review found three missed constructors in the existing SDK/Core
lifecycle fixture. They now use the actual describe result. All four
cases in that real PostgreSQL and worker RPC file passed.
- The first GitHub attempt failed in the unchanged GitHub recovery
pagination case in `chat-channels.integration.test.ts`: its zero-request
assertion observed a configuration GET. That exact case passed locally
without code or assertion changes. The one failed-job-only retry passed;
the initial failure log is retained.
- [GitHub workflow
42082587576](https://github.com/paperclipai/paperclip/actions/runs/42082587576)
passed on its second attempt. All CI checks completed, and Snyk passed.
Standard Greptile scored exact head `fb914d98b99e` 5/5 with no
unresolved threads. The branch is mergeable and ready for review.

## Risks

The task context change is internal. It adds no plugin wire field,
schema or Runner mode. A stale owner now gets an error and cannot clean
up a replacement. A new owner can still clean up that task. The retained
checkpoint write holds one existing lease row during a bounded local
file write.

Repeated stopped-source incarnation admission, runtime pins and
deployments are outside this change.

## Model Used

OpenAI GPT-6.1 Sol (`gpt-6.1-sol`), high reasoning. Used repository
tools, TypeScript and real PostgreSQL tests.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used with version and capability
details
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have described the issue in-PR using the bug template
- [x] I have not referenced internal or instance-local Paperclip issues
or links
- [x] My branch name describes the change
- [x] I have run the focused tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation
- [x] I have considered and documented risks
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no unresolved findings
- [x] I will address reviewer comments before requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/services/plugin-task-credential-writeback.ts

@@ -24,7 +24,7 @@ const handoffSchema = z.object({
   state: z.enum(["pending", "complete"]),
 }).strict();
 const key = "runnerTaskCredentialHandoff";
-type Scope = { companyId: string; leaseId: string };
+type Scope = { companyId: string; leaseId: string; expectedTaskId?: string };
 
 /** Save authority, never credential bytes or a controller-local temporary path. */
 export async function registerPluginTaskCredentialHandoff(
@@ -126,13 +126,15 @@ export async function settlePluginTaskCredentialHandoff(
       metadata: sql`coalesce(${environmentLeases.metadata}, '{}'::jsonb) || ${JSON.stringify({ [key]: { ...handoff, state: "complete" } })}::jsonb`,
     }).where(and(
       eq(environmentLeases.companyId, scope.companyId), eq(environmentLeases.id, scope.leaseId),
+      scope.expectedTaskId === undefined ? undefined : eq(environmentLeases.providerLeaseId, scope.expectedTaskId),
       sql`${environmentLeases.metadata}->${key} = ${JSON.stringify(handoff)}::jsonb`,
     )).returning({ id: environmentLeases.id });
     if (completed.length !== 1) {
-      const [current] = await db.select({ metadata: environmentLeases.metadata }).from(environmentLeases).where(and(
+      const [current] = await db.select({ metadata: environmentLeases.metadata, taskId: environmentLeases.providerLeaseId }).from(environmentLeases).where(and(
         eq(environmentLeases.companyId, scope.companyId), eq(environmentLeases.id, scope.leaseId),
       ));
-      if (!isDeepStrictEqual(handoffSchema.safeParse(current?.metadata?.[key]).data, { ...handoff, state: "complete" })) {
+      if (scope.expectedTaskId !== undefined && current?.taskId !== scope.expectedTaskId ||
+          !isDeepStrictEqual(handoffSchema.safeParse(current?.metadata?.[key]).data, { ...handoff, state: "complete" })) {
         throw new Error("Plugin task credential handoff changed");
       }
     }